Converting Variadic template pack into std::initializer_list

Question

Assume that there is a function which accepts several strings:

void fun (const std::initializer_list& strings) {
  for(auto s : strings)
          


        

Answer 1

Here's an answer to both points:

#include 
#include 
#include 
#include 

using namespace std;

void fun (const std::initializer_list& strings) {
  for(auto s : strings)
    cout << s << endl;
}

// This uses SFINAE to find if there's a string T::value in T
template 
struct HasValue
{
    typedef char OK; //sizeof() guaranteed 1
    struct BAD { char x[2]; }; //sizeof() guaranteed >1

    template 
    struct Helper;

    template 
    static OK has(X*, Helper<&X::value>* = nullptr); //SF if &X::value is not a const string*

    static BAD has(...);  //will be picked in SF case

    static const bool value = (sizeof(has((T*)nullptr)) == sizeof(OK));
};


// This template (and its specialisation) ensure all args have ::value
template 
struct HaveValue : public integral_constant::value && HaveValue::value>
{};

template 
struct HaveValue : public HasValue
{};



template 
void foo() {
    static_assert(HaveValue::value, "All arguments must have const string ::value");
    fun({Args::value...});  //answer to point 2: create the initialiser list
}

// Example data follow
struct A
{
    static const string value;
};
const string A::value = "AA";

struct B
{
    static const string value;
};
const string B::value = "BB";

struct C{};

int main()
{
    foo();
    //foo();  //uncomment to have the static assertion fire
}

See it live.